Correlated electron material devices using dopant species diffused from nearby structures

ABSTRACT

Subject matter disclosed herein may relate to fabrication of correlated electron materials used, for example, to perform a switching function. In embodiments, a correlated electron material may be doped using dopant species derived from one or more precursors utilized to fabricate nearby structures such as, for example, a conductive substrate or a conductive overlay.

BACKGROUND Field

This disclosure relates to correlated electron devices, and may relate,more particularly, to approaches toward fabricating correlated electrondevices, such as may be used in switches, memory circuits, and so forth,exhibiting desirable impedance characteristics.

Information

Integrated circuit devices, such as electronic switching devices, forexample, may be found in a wide range of electronic device types. Forexample, memory and/or logic devices may incorporate electronic switchessuitable for use in computers, digital cameras, cellular telephones,tablet devices, personal digital assistants, and so forth. Factorsrelated to electronic switching devices, which may be of interest to adesigner in considering whether an electronic switching device issuitable for a particular application, may include physical size,storage density, operating voltages, impedance ranges, and/or powerconsumption, for example. Other factors that may be of interest todesigners may include, for example, cost of manufacture, ease ofmanufacture, scalability, and/or reliability. Moreover, there appears tobe an ever-increasing need for memory and/or logic devices that exhibitcharacteristics of lower power and/or higher speed.

BRIEF DESCRIPTION OF THE DRAWINGS

Claimed subject matter is particularly pointed out and distinctlyclaimed in the concluding portion of the specification. However, both asto organization and/or method of operation, together with objects,features, and/or advantages thereof, it may best be understood byreference to the following detailed description if read with theaccompanying drawings in which:

FIG. 1A is an illustration of an embodiment of a current density versusvoltage profile of a device formed from a correlated electron material;

FIG. 1B is an illustration of an embodiment of a switching devicecomprising a correlated electron material and a schematic diagram of anequivalent circuit of a correlated electron material switch;

FIG. 2A is an illustration of an embodiment of a conductive substrateshowing dopant species atoms;

FIG. 2B is an illustration of an embodiment of a correlated electronmaterial receiving dopant species atoms responsive to doping of theconductive substrate;

FIG. 2C is an illustration of an embodiment of a conductive substratedeposited over a correlated electron material (CEM) film;

FIG. 2D is an illustration of an embodiment of a correlated electronmaterial receiving dopant species atoms responsive to doping of theconductive overlay;

FIG. 3A is an illustration of an embodiment of an example precursor,utilized to form a conductive substrate material, along with one or moretypes of dopant species molecules;

FIG. 3B is an illustration of an embodiment of dopant species moleculesembedded in a conductive material diffusing to a CEM film; and

FIGS. 4 and 5 are flowcharts of embodiments for generalized processesfor fabricating a correlated electron material with reduced interfaciallayer impedance.

Reference is made in the following detailed description to accompanyingdrawings, which form a part hereof, wherein like numerals may designatelike parts throughout that are corresponding and/or analogous. It willbe appreciated that the figures have not necessarily been drawn toscale, such as for simplicity and/or clarity of illustration. Forexample, dimensions of some aspects may be exaggerated relative toothers. Further, it is to be understood that other embodiments may beutilized. Furthermore, structural and/or other changes may be madewithout departing from claimed subject matter. References throughoutthis specification to “claimed subject matter” refer to subject matterintended to be covered by one or more claims, or any portion thereof,and are not necessarily intended to refer to a complete claim set, to aparticular combination of claim sets (e.g., method claims, apparatusclaims, etc.), or to a particular claim. It should also be noted thatdirections and/or references, for example, such as up, down, top,bottom, and so on, may be used to facilitate discussion of drawings andare not intended to restrict application of claimed subject matter.Therefore, the following detailed description is not to be taken tolimit claimed subject matter and/or equivalents.

DETAILED DESCRIPTION

References throughout this specification to one implementation, animplementation, one embodiment, an embodiment, and/or the like meansthat a particular feature, structure, characteristic, and/or the likedescribed in relation to a particular implementation and/or embodimentis included in at least one implementation and/or embodiment of claimedsubject matter. Thus, appearances of such phrases, for example, invarious places throughout this specification are not necessarilyintended to refer to the same implementation and/or embodiment or to anyone particular implementation and/or embodiment. Furthermore, it is tobe understood that particular features, structures, characteristics,and/or the like described are capable of being combined in various waysin one or more implementations and/or embodiments and, therefore, arewithin intended claim scope. In general, of course, as has been the casefor the specification of a patent application, these and other issueshave a potential to vary in a particular context of usage. In otherwords, throughout the disclosure, particular context of descriptionand/or usage provides helpful guidance regarding reasonable inferencesto be drawn; however, likewise, “in this context” in general withoutfurther qualification refers to the context of the present disclosure.

Particular aspects of the present disclosure describe methods and/orprocesses for preparing and/or fabricating correlated electron materials(CEMs) to form, for example, a correlated electron switch, such as maybe utilized to form a correlated electron random access memory (CERAM)in memory and/or logic devices, for example. CEMs, which may be utilizedin the construction of CERAM devices and CEM switches, for example, mayalso comprise a wide range of other electronic circuit types, such as,for example, memory controllers, memory arrays, filter circuits, dataconverters, optical instruments, phase locked loop circuits, microwaveand millimeter wave transceivers, and so forth, although claimed subjectmatter is not limited in scope in these respects. In this context, a CEMswitch may exhibit a substantially rapid conductor-to-insulatortransition, which may be brought about by electron correlations ratherthan solid state structural phase changes, such as in response to achange from a crystalline state to an amorphous state, for example, in aphase change memory device or, in another example, formation offilaments in resistive RAM devices. In one aspect, a substantially rapidconductor-to-insulator transition in a CEM device may be responsive to aquantum mechanical phenomenon, in contrast to melting/solidification orfilament formation, for example, in phase change and resistive RAMdevices. Such quantum mechanical transitions between relativelyconductive and relatively insulative states, and/or between first andsecond impedance states, for example, in a CEM may be understood in anyone of several aspects. As used herein, the terms “relatively conductivestate,” “relatively lower impedance state,” and/or “metal state” may beinterchangeable, and/or may, at times, be referred to as a “relativelyconductive/lower impedance state.” Similarly, the terms “relativelyinsulative state” and “relatively higher impedance state” may be usedinterchangeably herein, and/or may, at times, be referred to as arelatively “insulative/higher impedance state.”

In an aspect, a quantum mechanical transition of a correlated electronmaterial between a relatively insulative/higher impedance state and arelatively conductive/lower impedance state, wherein the relativelyconductive/lower impedance state is substantially dissimilar from theinsulated/higher impedance state, may be understood in terms of a Motttransition. In accordance with a Mott transition, a material may switchfrom a relatively insulative/higher impedance state to a relativelyconductive/lower impedance state if a Mott transition condition occurs.The Mott criteria may be defined by (n_(c))^(1/3)a≈0.26, wherein n_(c)denotes a concentration of electrons, and wherein “a” denotes the Bohrradius. If a threshold carrier concentration is achieved, such that theMott criteria is met, the Mott transition is believed to occur.Responsive to the Mott transition occurring, the state of the CEM devicechanges from a relatively higher resistance/higher capacitance state(e.g., an insulative/higher impedance state) to a relatively lowerresistance/lower capacitance state (e.g., a conductive/lower impedancestate) that is substantially dissimilar from the higherresistance/higher capacitance state.

In another aspect, the Mott transition may be controlled by alocalization of electrons. If carriers, such as electrons, for example,are localized, a strong coulomb interaction between the carriers isbelieved to split the bands of the CEM to bring about a relativelyinsulative (relatively higher impedance) state. If electrons are nolonger localized, a weak coulomb interaction may dominate, which maygive rise to a removal of band splitting, which may, in turn, bringabout a metal (conductive) band (relatively lower impedance state) thatis substantially dissimilar from the relatively higher impedance state.

Further, in an embodiment, switching from a relatively insulative/higherimpedance state to a substantially dissimilar and relativelyconductive/lower impedance state may bring about a change in capacitancein addition to a change in resistance. For example, a CEM device mayexhibit a variable resistance together with a property of variablecapacitance. In other words, impedance characteristics of a CEM devicemay comprise a “complex” impedance, which may include both resistive andcapacitive components. For example, in a metal state, a CEM device maycomprise a relatively low electric field that may approach zero, andtherefore may exhibit a substantially low capacitance (e.g., relativelylow complex impedance), which may likewise approach zero.

Similarly, in a relatively insulative/higher impedance state, which maybe brought about by a higher density of bound or correlated electrons,an external electric field may be capable of penetrating the CEM and,therefore, the CEM may exhibit higher capacitance based, at least inpart, on additional charges stored within the CEM. Thus, for example, atransition from a relatively insulative/higher impedance state (e.g.,relatively high complex impedance) to a substantially dissimilar andrelatively conductive/lower impedance state in a CEM device may resultin changes in both resistance and capacitance, at least in particularembodiments. Such a transition may bring about additional measurablephenomena, and claimed subject matter is not limited in this respect.

In an embodiment, a device formed from a CEM may exhibit switching ofimpedance states responsive to a Mott-transition in a majority of thevolume of the CEM comprising a device. In an embodiment, a CEM may forma “bulk switch.” As used herein, the term “bulk switch” refers to atleast a majority volume of a CEM switching a device's impedance state,such as in response to a Mott-transition. For example, in an embodiment,substantially all CEM of a device may switch from a relativelyinsulative/higher impedance state to a relatively conductive/lowerimpedance state or from a relatively conductive/lower impedance state toa relatively insulative/higher impedance state responsive to aMott-transition. In an embodiment, a CEM may comprise one or moretransition metals, or more transition metal compounds, one or moretransition metal oxides (TMOs), one or more oxides comprising rare earthelements, one or more oxides of one or more f-block elements of theperiodic table, one or more rare earth transitional metal oxideperovskites, yttrium, and/or ytterbium, although claimed subject matteris not limited in scope in this respect. In an embodiment, a CEM devicemay comprise one or more materials selected from a group comprisingaluminum, cadmium, chromium, cobalt, copper, gold, iron, manganese,mercury, molybdenum, nickel, palladium, rhenium, ruthenium, silver,tantalum, tin, titanium, vanadium, yttrium, and zinc (which may belinked to an anion, such as oxygen or other types of ligands), orcombinations thereof, although claimed subject matter is not limited inscope in this respect.

FIG. 1A is an illustration of an embodiment 100 of a current densityversus voltage profile of a device formed from a CEM. Based, at least inpart, on a voltage applied to terminals of a CEM device, for example,during a “write operation,” the CEM device may be placed into arelatively low-impedance state or a relatively high-impedance state. Forexample, application of a voltage V_(set) and a current density J_(set)may bring about a transition of the CEM device to a relativelylow-impedance memory state. Conversely, application of a voltageV_(reset) and a current density J_(reset) may bring about a transitionof the CEM device to a relatively high-impedance memory state. As shownin FIG. 1A, reference designator 110 illustrates the voltage range thatmay separate V_(set) from V_(reset). Following placement of the CEMdevice into a high-impedance state or a low-impedance state, theparticular state of the CEM device may be detected by application of avoltage V_(read) (e.g., during a read operation) and detection of acurrent or current density at terminals of the CEM device (e.g.,utilizing read window 107).

According to an embodiment, the CEM device characterized in FIG. 1A maycomprise any transition metal oxide (TMO), such as, for example,perovskites, Mott insulators, charge exchange insulators, and Andersondisorder insulators. In particular implementations, a CEM device may beformed from switching materials, such as nickel oxide, cobalt oxide,iron oxide, yttrium oxide, titanium yttrium oxide, and perovskites, suchas chromium doped strontium titanate, lanthanum titanate, and themanganate family including praseodymium calcium manganate, andpraseodymium lanthanum manganite, just to provide a few examples. Inparticular, oxides incorporating elements with incomplete “d” and “f”orbital shells may exhibit sufficient impedance switching properties foruse in a CEM device. Other implementations may employ other transitionmetal compounds without deviating from claimed subject matter.

In one aspect, the CEM device of FIG. 1A may comprise other types oftransition metal oxide variable impedance materials, though it should beunderstood that these are exemplary only and are not intended to limitclaimed subject matter. Nickel oxide (NiO) is disclosed as oneparticular TMO. NiO materials discussed herein may be doped withextrinsic ligands, which may establish and/or stabilize variableimpedance properties. Thus, in another particular example, NiO dopedwith extrinsic ligands may be expressed as NiO:L_(x), where L_(x) mayindicate a ligand element or compound and x may indicate a number ofunits of the ligand for one unit of NiO. A value of x may be determinedfor any specific ligand and any specific combination of ligand with NiOor with any other transition metal compound simply by balancingvalences. Other dopant ligands in addition to carbonyl may include:nitrosyl (NO), triphenylphosphine (PPH₃), phenanthroline (C₁₂H₈N₂),bipyridine (C₁₀H₈N₂), ethylenediamine (C₂H₄(NH₂)₂), ammonia (NH₃),acetonitrile (CH₃CN), Fluoride (F), Chloride (Cl), Bromide (Br), cyanide(CN), sulfur (S) and others.

In another embodiment, the CEM device of FIG. 1A may comprise othertransition metal oxide variable impedance materials, such asnitrogen-containing ligands, though it should be understood that theseare exemplary only and are not intended to limit claimed subject matter.Nickel oxide (NiO) is disclosed as one particular TMO. NiO materialsdiscussed herein may be doped with extrinsic nitrogen-containingligands, which may stabilize variable impedance properties. Inparticular, NiO variable impedance materials disclosed herein mayinclude nitrogen-containing molecules of the form C_(x)H_(y)N_(z)(wherein x≥0, y≥0, z≥0, and wherein at least x, y, or z comprisevalues >0) such as: ammonia (NH₃), cyano (CN⁻), azide ion (N₃ ⁻)ethylene diamine (C₂H₈N₂), phen(1,10-phenanthroline) (C₁₂H₈N₂),2,2′bipyridine (C₁₀,H₈N₂), ethylenediamine ((C₂H₄(NH₂)₂), pyridine(C₅H₅N), acetonitrile (CH₃CN), and cyanosulfanides such as thiocyanate(NCS⁻), for example. NiO variable impedance materials disclosed hereinmay include members of an oxynitride family (N_(x)O_(y), wherein x and ycomprise whole numbers, and wherein x≥0 and y≥0 and at least x or ycomprise values >0), which may include, for example, nitric oxide (NO),nitrous oxide (N₂O), nitrogen dioxide (NO₂), or precursors with an NO₃ ⁻ligand. In embodiments, metal precursors comprising nitrogen-containingligands, such as ligands amines, amides, alkylamides nitrogen-containingligands with NiO by balancing valences.

In accordance with FIG. 1A, if sufficient bias is applied (e.g.,exceeding a band-splitting potential) and the aforementioned Mottcondition is satisfied (e.g., injected electron holes are of apopulation comparable to a population of electrons in a switchingregion, for example), a CEM device may switch from a relativelylow-impedance state to a relatively high-impedance state, for example,responsive to a Mott transition. This may correspond to point 108 of thevoltage versus current density profile of FIG. 1A. At, or suitablynearby this point, electrons are no longer screened and become localizednear the metal ion. This correlation may result in a strongelectron-to-electron interaction potential, which may operate to splitthe bands to form a relatively high-impedance material. If the CEMdevice comprises a relatively high-impedance state, current may begenerated by transportation of electron holes. Consequently, if athreshold voltage is applied across terminals of the CEM device,electrons may be injected into a metal-insulator-metal (MIM) diode overthe potential barrier of the MIM device. In certain embodiments,injection of a threshold current of electrons, at a threshold potentialapplied across terminals of a CEM device, may perform a “set” operation,which places the CEM device into a low-impedance state. In alow-impedance state, an increase in electrons may screen incomingelectrons and remove a localization of electrons, which may operate tocollapse the band-splitting potential, thereby giving rise to thelow-impedance state.

According to an embodiment, current in a CEM device may be controlled byan externally applied “compliance” condition, which may be determined atleast partially on the basis of an applied external current, which maybe limited during a write operation, for example, to place the CEMdevice into a relatively high-impedance state. This externally-appliedcompliance current may, in some embodiments, also set a condition of acurrent density for a subsequent reset operation to place the CEM deviceinto a relatively high-impedance state. As shown in the particularimplementation of FIG. 1A, a current density J_(comp) may be appliedduring a write operation at point 116 to place the CEM device into arelatively high-impedance state, may determine a compliance conditionfor placing the CEM device into a low-impedance state in a subsequentwrite operation. As shown in FIG. 1A, the CEM device may be subsequentlyplaced into a low-impedance state by application of a current densityJ_(reset)≥J_(comp) at a voltage V_(reset) at point 108, at whichJ_(comp) is externally applied.

In embodiments, compliance may set a number of electrons in a CEMdevice, which may be “captured” by holes for the Mott transition. Inother words, a current applied in a write operation to place a CEMdevice into a relatively low-impedance memory state may determine anumber of holes to be injected to the CEM device for subsequentlytransitioning the CEM device to a relatively high-impedance memorystate.

As pointed out above, a reset condition may occur in response to a Motttransition at point 108. As pointed out above, such a Mott transitionmay bring about a condition in a CEM device in which a concentration ofelectrons n approximately equals, or becomes at least comparable to, aconcentration of electron holes p. This condition may be modeledaccording to expression (1) as follows:

$\begin{matrix}{{{\lambda_{TF}n^{\frac{1}{3}}} = {C \sim 0.26}}{n = \left( \frac{C}{\lambda_{TF}} \right)^{3}}} & (1)\end{matrix}$

In expression (1), λ_(TF) corresponds to a Thomas Fermi screeninglength, and C is a constant.

According to an embodiment, a current or current density in region 104of the voltage versus current density profile shown in FIG. 1A, mayexist in response to injection of holes from a voltage signal appliedacross terminals of a CEM device. Here, injection of holes may meet aMott transition criterion for the low-impedance state to high-impedancestate transition at current I_(MI) as a threshold voltage V_(MI) isapplied across terminals of a CEM device. This may be modeled accordingto expression (2) as follows:

$\begin{matrix}{{{I_{MI}\left( V_{MI} \right)} = {\frac{{dQ}\left( V_{MI} \right)}{dt} \approx \frac{Q\left( V_{MI} \right)}{t}}}{{Q\left( V_{MI} \right)} = {{qn}\left( V_{MI} \right)}}} & (2)\end{matrix}$

Where Q(V_(MI)) corresponds to the charged injected (holes or electrons)and is a function of an applied voltage. Injection of electrons and/orholes to enable a Mott transition may occur between bands and inresponse to threshold voltage V_(MI), and threshold current I_(MI). Byequating electron concentration n with a charge concentration to bringabout a Mott transition by holes injected by I_(MI) in expression (2)according to expression (1), a dependency of such a threshold voltageV_(MI) on Thomas Fermi screening length λ_(TF) may be modeled accordingto expression (3), as follows:

$\begin{matrix}{{{I_{MI}\left( V_{MI} \right)} = {\frac{Q\left( V_{MI} \right)}{t} = {\frac{{qn}\left( V_{MI} \right)}{t} = {\frac{q}{t}\left( \frac{C}{\lambda_{TF}} \right)^{3}}}}}{{J_{reset}\left( V_{MI} \right)} = {{J_{MI}\left( V_{MI} \right)} = {\frac{I_{MI}\left( V_{MI} \right)}{A_{CEM}} = {\frac{q}{A_{CEM}t}\left( \frac{C}{\lambda_{TF}\left( V_{MI} \right)} \right)^{3}}}}}} & (3)\end{matrix}$

In which A_(CEM) is a cross-sectional area of a CEM device; andJ_(reset)(V_(MI)), may represent a current density through the CEMdevice to be applied to the CEM device at a threshold voltage V_(MI),which may place the CEM device into a relatively high-impedance state.

FIG. 1B is an illustration of an embodiment 150 of a switching devicecomprising a correlated electron material and a schematic diagram of anequivalent circuit of a correlated electron material switch. Aspreviously mentioned, a correlated electron device, such as a CEMswitch, a CERAM array, or other type of device utilizing one or morecorrelated electron materials may comprise variable or complex impedancedevice that may exhibit characteristics of both variable resistance andvariable capacitance. In other words, impedance characteristics for aCEM variable impedance device, such as a device comprising a conductivesubstrate 160, CEM 170, and conductive overlay 180, may depend at leastin part on resistance and capacitance characteristics of the device ifmeasured across device terminals 122 and 130. In an embodiment, anequivalent circuit for a variable impedance device may comprise avariable resistor, such as variable resistor 126, in parallel with avariable capacitor, such as variable capacitor 128. Of course, althougha variable resistor 126 and variable capacitor 128 are depicted in FIG.1B as comprising discrete components, a variable impedance device, suchas device of embodiment 150, may comprise a substantially homogenous CEMand claimed subject matter is not limited in this respect.

Table 1 below depicts an example truth table for an example variableimpedance device, such as the device of embodiment 150.

TABLE 1 Correlated Electron Switch Truth Table Resistance CapacitanceImpedance R_(high)(V_(applied)) C_(high)(V_(applied))Z_(high)(V_(applied)) R_(low)(V_(applied)) C_(low)(V_(applied))~0Z_(low)(V_(applied))

In an embodiment, Table 1 shows that a resistance of a variableimpedance device, such as the device of embodiment 150, may transitionbetween a low-impedance state and a substantially dissimilar,high-impedance state as a function at least partially dependent on avoltage applied across the CEM device. In an embodiment, an impedanceexhibited at a low-impedance state may be approximately in the range of10.0-100,000.0 times lower than an impedance exhibited in ahigh-impedance state. In other embodiments, an impedance exhibited at alow-impedance state may be approximately in the range of 5.0 to 10.0times lower than an impedance exhibited in a high-impedance state, forexample. It should be noted, however, that claimed subject matter is notlimited to any particular impedance ratios between high-impedance statesand low-impedance states. Table 1 shows that a capacitance of a variableimpedance device, such as the device of embodiment 150, may transitionbetween a lower capacitance state, which, in an example embodiment, maycomprise approximately zero, or very little, capacitance, and a highercapacitance state that is a function, at least in part, of a voltageapplied across the CEM device.

According to an embodiment, a CEM device, which may be utilized to forma CEM switch, a CERAM memory device, or a variety of other electronicdevices comprising one or more correlated electron materials, may beplaced into a relatively low-impedance memory state, such as bytransitioning from a relatively high-impedance state, for example, viainjection of a sufficient quantity of electrons to satisfy a Motttransition criteria. In transitioning a CEM device to a relativelylow-impedance state, if enough electrons are injected and the potentialacross the terminals of the CEM device overcomes a threshold switchingpotential (e.g., V_(set)), injected electrons may begin to screen. Aspreviously mentioned, screening may operate to unlocalizedouble-occupied electrons to collapse the band-splitting potential,thereby bringing about a relatively low-impedance state.

In particular embodiments, changes in impedance states of CEM devices,such as changes from a low-impedance state to a substantially dissimilarhigh-impedance state, for example, may be brought about by“back-donation” of electrons of compounds comprising NiO_(x)O_(y)(wherein the subscripts “x” and “y” comprise whole numbers). As the termis used herein, “back-donation” refers to a supplying of one or moreelectrons to a transition metal, transition metal oxide, or anycombination thereof, by an adjacent molecule of a lattice structure, forexample, comprising the transition metal, transition metal compound,transition metal oxide, or comprising a combination thereof.Back-donation may permit a transition metal, transition metal compound,transition metal oxide, or a combination thereof, to maintain anionization state that is favorable to electrical conduction under aninfluence of an applied voltage. In certain embodiments, back-donationin a CEM, for example, may occur responsive to use of carbonyl (CO) ormay occur responsive to use of a nitrogen-containing dopant, such asammonia (NH₃), ethylene diamine (C₂H₈N₂), or members of an oxynitridefamily (N_(x)O_(y)), for example, which may permit a CEM to exhibit aproperty in which electrons are controllably, and reversibly, “donated”to a conduction band of the transition metal or transition metal oxide,such as nickel, for example, during operation of a device or circuitcomprising a CEM. Back donation may be reversed, for example, in nickeloxide material (e.g., NiO:CO or NiO:NH₃), thereby permitting the nickeloxide material to switch to exhibiting a substantially dissimilarimpedance property, such as a high-impedance property, during deviceoperation.

Thus, in this context, a back-donating material refers to a materialthat exhibits an impedance switching property, such as switching from afirst impedance state to a substantially dissimilar second impedancestate (e.g., from a relatively low impedance state to a relatively highimpedance state, or vice versa) based, at least in part, on influence ofan applied voltage to control donation of electrons, and reversal of theelectron donation, to and from a conduction band of the material.

In some embodiments, by way of back-donation, a CEM switch comprising atransition metal, transition metal compound, or a transition metaloxide, may exhibit low-impedance properties if the transition metal,such as nickel, for example, is placed into an oxidation state of2+(e.g., Ni²⁺ in a material, such as NiO:CO or NiO:NH₃). Conversely,electron back-donation may be reversed if a transition metal, such asnickel, for example, is placed into an oxidation state of 1+ or 3+.Accordingly, during operation of a CEM device, back-donation may resultin “disproportionation,” which may comprise substantially simultaneousoxidation and reduction reaction, substantially in accordance withexpression (4), below:

2Ni²⁺→Ni¹⁺+Ni³⁺  (4)

Such disproportionation, in this instance, refers to formation of nickelions as Ni¹⁺+Ni³⁺ as shown in expression (4), which may bring about, forexample, a relatively high-impedance state during operation of the CEMdevice. In an embodiment, a “dopant” such as a carbon-containing ligand,carbonyl (CO) or a nitrogen-containing ligand, such as an ammoniamolecule (NH₃), may permit sharing of electrons during operation of theCEM device so as to give rise to the disproportionation reaction ofexpression (4), and its reversal, substantially in accordance withexpression (5), below:

Ni¹⁺+Ni³⁺→2Ni²⁺  (5)

As previously mentioned, reversal of the disproportionation reaction, asshown in expression (5), permits nickel-based CEM to return to arelatively low-impedance state.

As the term is used herein, a “dominant” ligand may refer to a ligandthat gives rise to a “p-type” CEM by way of back-donation with a metalion as described in expression (4). Accordingly, in particularembodiments, a CEM material may be expressed in a metal-ligand form (ML)such as, for example, NiO in which Ni corresponds to the metal “M” andin which O corresponds to the ligand “L.” In another example, such as aCEM utilizing vanadium oxide (VO), V may correspond to the metal “M” and“O” may correspond to the ligand “L.”

In embodiments, depending on a molecular concentration of NiO:CO orNiO:NH₃, for example, which may vary from values approximately in therange of an atomic percentage of 0.1% to 10.0%, V_(reset) and V_(set),as shown in FIG. 1A, may vary approximately in the range of 0.1 V to10.0 V subject to the condition that V_(set)≥V_(reset). For example, inone possible embodiment, V_(reset) may occur at a voltage approximatelyin the range of 0.1 V to 1.0 V, and V_(set) may occur at a voltageapproximately in the range of 1.0 V to 2.0 V, for example. It should benoted, however, that variations in V_(set) and V_(reset) may occurbased, at least in part, on a variety of factors, such as atomicconcentration of a back-donating material, such as NiO:CO or NiO:NH₃ andother materials present in the CEM device, as well as other processvariations, and claimed subject matter is not limited in this respect.

In certain embodiments, atomic layer deposition may be utilized to formor to fabricate films comprising nickel oxide materials, such as NiO:COor NiO:NH₃, to permit electron back-donation during operation of the CEMdevice in a circuit environment, for example, to give rise to alow-impedance state. Also during operation in a circuit environment, forexample, electron back-donation may be reversed so as to give rise to asubstantially dissimilar impedance state, such as a high-impedancestate, for example. In particular embodiments, atomic layer depositionmay utilize two or more precursors to deposit components of, forexample, NiO:CO or NiO:NH₃, or other transition metal oxide, transitionmetal, or combination thereof, onto a conductive substrate. In anembodiment, layers of a CEM device may be deposited utilizing separateprecursor molecules, AX and BY, according to expression (6a), below:

AX_((gas))+BY_((gas))=AB_((solid))+XY_((gas))  (6a)

Wherein “A” of expression (6a) corresponds to a transition metal,transition metal compound, transition metal oxide, or any combinationthereof. In embodiments, a transition metal oxide may comprise nickel,but may comprise other transition metals, transition metal compound,and/or transition metal oxides, such as aluminum, cadmium, chromium,cobalt, copper, gold, iron, manganese, mercury, molybdenum, nickelpalladium, rhenium, ruthenium, silver, tin, titanium, vanadium. Inparticular embodiments, compounds that comprise more than one transitionmetal oxide may also be utilized, such as yttrium titanate (YTiO₃).

In embodiments, “X” of expression (6a) may comprise a ligand, such asorganic ligand, comprising amidinate (AMD), dicyclopentadienyl (Cp)₂,diethylcyclopentadienyl (EtCp)₂,Bis(2,2,6,6-tetramethylheptane-3,5-dionato) ((thd)₂), acetylacetonate(acac), bis(methylcyclopentadienyl) ((CH₃C₅H₄)₂), dimethylglyoximate(dmg)₂, 2-amino-pent-2-en-4-onato (apo)₂, (dmamb)₂ wheredmamb=1-dimethylamino-2-methyl-2-butanolate, (dmamp)2 wheredmamp=1-dimethylamino-2-methyl-2-propanolate,Bis(pentamethylcyclopentadienyl) (C₅(CH₃)₅)₂ and carbonyl (CO)₄.Accordingly, in some embodiments, nickel-based precursor AX maycomprise, for example, nickel amidinate (Ni(AMD)), nickeldicyclopentadienyl (Ni(Cp)₂), nickel diethylcyclopentadienyl(Ni(EtCp)₂), Bis(2,2,6,6-tetramethylheptane-3,5-dionato)Ni(II)(Ni(thd)₂), nickel acetylacetonate (Ni(acac)₂),bis(methylcyclopentadienyl)nickel (Ni(CH₃C₅H₄)₂, Nickeldimethylglyoximate (Ni(dmg)₂), Nickel 2-amino-pent-2-en-4-onato(Ni(apo)₂), Ni(dmamb)₂ wheredmamb=1-dimethylamino-2-methyl-2-butanolate, Ni(dmamp)₂ wheredmamp=1-dimethylamino-2-methyl-2-propanolate,Bis(pentamethylcyclopentadienyl) nickel (Ni(C₅(CH₃)₅)₂, and nickelcarbonyl (Ni(CO)₄), just to name a few examples. In expression (6a),precursor “BY” may comprise an oxidizer, such as oxygen (O₂), ozone(O₃), nitric oxide (NO), hydrogen peroxide (H₂O₂), just to name a fewexamples. In other embodiments, plasma may be used with an oxidizer toform oxygen radicals.

However, in particular embodiments, a dopant in addition to precursorsAX and BY may be utilized to form layers of the CEM device. Anadditional dopant ligand, which may co-flow with precursor AX, maypermit formation of back-donating compounds, substantially in accordancewith expression (6b), below. In embodiments, dopants such as ammonia(NH₃), methane (CH₄), carbon monoxide (CO), or other may be utilized, asmay other ligands comprising carbon or nitrogen or the other dopantslisted above. Thus, expression (6a) may be modified to include anadditional dopant ligand substantially in accordance with expression(6b), below:

$\begin{matrix}{{{AX}_{({gas})} + \left( {{NH}_{3}\mspace{14mu} {or}\mspace{14mu} {other}\mspace{14mu} {ligand}\mspace{14mu} {comprising}\mspace{14mu} {nitrogen}} \right) + {BY}_{({gas})}} = {{{AB}\text{:}{NH}_{3{({solid})}}} + {XY}_{({gas})}}} & \left( {6b} \right)\end{matrix}$

It should be noted that concentrations, such as atomic concentration, ofprecursors, such as AX, BY, and NH₃ (or other ligand comprisingnitrogen) of expressions (6a) and (6b) may be adjusted so as to bringabout a final atomic concentration of nitrogen or carbon dopant in afabricated CEM device, such as in the form of ammonia (NH₃) or carbonyl(CO) of between approximately 0.1% and 10.0%. However, claimed subjectmatter is not necessarily limited to the above-identified precursorsand/or atomic concentrations. Rather, claimed subject matter is intendedto embrace all such precursors utilized in atomic layer deposition,chemical vapor deposition, plasma chemical vapor deposition, sputterdeposition, physical vapor deposition, hot wire chemical vapordeposition, laser enhanced chemical vapor deposition, laser enhancedatomic layer deposition, rapid thermal chemical vapor deposition, spinon deposition or the like, utilized in fabrication of CEM devices. Inexpressions (6a) and (6b), “BY” may comprise an oxidizer, such as oxygen(O₂), ozone (O₃), nitric oxide (NO), hydrogen peroxide (H₂O₂), just toname a few examples. In other embodiments, plasma may be used with anoxidizer (BY) to form oxygen radicals. Likewise, plasma may be used withthe doping species to form an activated species that will control thedoping concentration of the CEM.

In particular embodiments, such as embodiments utilizing atomic layerdeposition, a CEM film may be exposed to precursors, such as AX and BY,as well as dopant species molecules (such as ammonia or other ligandscomprising metal-nitrogen bonds, including, for example, nickel-amides,nickel-imides, nickel-amidinates, or combinations thereof) in a heatedchamber, which may attain, for example, a temperature approximately inthe range of 20.0° C. to 1000.0° C., for example, or betweentemperatures approximately in the range of 20.0° C. and 500.0° C. incertain embodiments. In one particular embodiment, in which atomic layerdeposition of NiO:NH₃, for example, is performed, temperature rangesapproximately in the range of 20.0° C. and 400.0° C. may be utilized.Responsive to exposure to precursor gases (e.g., AX, BY, NH₃ or otherligand comprising nitrogen), such gases may be purged from the heatedchamber for durations approximately in the range of 0.5 seconds to 180.0seconds. It should be noted, however, that these are merely examples ofpotentially suitable ranges of temperature and/or time and claimedsubject matter is not limited in this respect.

In certain embodiments, a single two-precursor cycle (e.g., AX and BY,as described with reference to expression 6(a)) or a singlethree-precursor cycle (e.g., AX, NH₃ or other ligand comprisingnitrogen, and BY, as described with reference to expression 6(b))utilizing atomic layer deposition may bring about a CEM device layercomprising a thickness approximately in the range of 0.6 Å to 1.5 Å).Accordingly, in an embodiment, to form a CEM device film comprising athickness of approximately 500.0 Å utilizing an atomic layer depositionprocess in which layers comprise a thickness of approximately 0.6 Å,800-900 cycles, for example, may be utilized. In another embodiment,utilizing an atomic layer deposition process in which layers compriseapproximately 1.5 Å, 300 to 350 two-precursor cycles, for example, maybe performed. It should be noted that atomic layer deposition may beutilized to form CEM device films having other thicknesses, such asthicknesses approximately in the range of 1.5 nm to 150.0 nm, forexample, and claimed subject matter is not limited in this respect.

In particular embodiments, responsive to one or more two-precursorcycles (e.g., AX and BY), or three-precursor cycles (AX, NH₃ or otherligand comprising nitrogen, and BY), of atomic layer deposition, a CEMdevice film may undergo in situ annealing, which may permit improvementof film properties or may be used to incorporate the material usingnitrogen as a dopant species, such as in the form of ammonia, in the CEMdevice film. In certain embodiments, a chamber may be heated to atemperature approximately in the range of 20.0° C. to 1000.0° C.However, in other embodiments, in situ annealing may be performedutilizing temperatures approximately in the range of 150.0° C. to 800.0°C. In situ annealing times may vary from a duration approximately in therange of 1.0 seconds to 5.0 hours. In particular embodiments, annealingtimes may vary within more narrow ranges, such as, for example, fromapproximately 0.5 minutes to approximately 180.0 minutes, for example,and claimed subject matter is not limited in these respects.

In particular embodiments, a CEM device manufactured in accordance withthe above-described process may exhibit a “born on” property in whichthe device exhibits relatively low impedance (relatively highconductivity) immediately after fabrication of the device. Accordingly,if a CEM device is integrated into a larger electronics environment, forexample, at initial activation a relatively small voltage applied to aCEM device may permit a relatively high current flow through the CEMdevice, as shown by region 104 of FIG. 1A. For example, as previouslydescribed herein, in at least one possible embodiment, V_(reset) mayoccur at a voltage approximately in the range of 0.1 V to 1.0 V, andV_(set) may occur at a voltage approximately in the range of 1.0 V to2.0 V, for example. Accordingly, electrical switching voltages operatingin a range of approximately 2.0 V, or less, may permit a memory circuit,for example, to write to a CERAM memory device, to read from a CERAMmemory device, or to change state of a CERAM switch, for example. Inembodiments, such relatively low voltage operation may reducecomplexity, cost, and may provide other advantages over competing memoryand/or switching device technologies.

FIG. 2A is an illustration of an embodiment 200 of a conductivesubstrate showing dopant species atoms. A conductive substrate, such asconductive substrate 210, for example, may comprise a titanium-basedand/or titanium-containing substrate, such as titanium nitride (TiN),fabricated in layers, for example, for use in a CERAM device or othertype of CEM-based device. In other embodiments, conductive substrate 210may comprise other types of conductive materials, such as titaniumnitride, platinum, titanium, copper, aluminum, cobalt, nickel, tungsten,tungsten nitride, cobalt silicide, ruthenium oxide, chromium, gold,palladium, indium tin oxide, tantalum, silver, iridium, or anycombination thereof, and claimed subject matter is not limited to anyparticular composition of conductive substrate material.

In embodiments, in which conductive substrate 210 comprises titaniumnitride, for example, substrate 210 may be formed utilizing precursorssuch as titanium tetrachloride (TiCl₄), which may comprise chlorine as apotential dopant species as the chlorine atoms diffuse into a CEM. Inanother embodiment, a TiN substrate may be formed utilizing tetrakisdimethylamido titanium (TDMAT), tetrakis diethylamido titanium (TDEAT),and/or titanium isopropoxide (TTIP), which may comprise carbon as adopant species as carbon atoms diffuse into the CEM. It should be notedthat titanium-based and/or titanium-containing precursor materials maycomprise dopant species in addition to chlorine and/or carbon andclaimed subject matter is not limited in this respect. Precursors may beused with nitrogen (e.g., co-flow) as a dopant species in the form ofNH₃.

In other embodiments, conductive substrate 210 may comprise atantalum-based and/or a tantalum-containing material, such as tantalumnitride (TaN), formed in layers, for use in a CERAM device or other typeof CEM-based device. In embodiments, a TaN substrate may be formedutilizing precursors such as pentakisdimethylamido tantalum (PDMAT),which may comprise carbon as a dopant species. In another embodiment, aTaN substrate may be formed utilizing tantalum ethoxide (TAETO), whichmay also comprise carbon as a dopant species. In another embodiment, aTaN substrate may be formed utilizing tantalum pentachloride (TaCl₅),which may comprise chlorine as a dopant species. It should be noted thattantalum-based and/or tantalum-containing precursor materials maycomprise dopant species in addition to chlorine and/or carbon andclaimed subject matter is not limited in this respect. Precursors may beused with nitrogen (e.g., co-flow) as a dopant species in the form ofNH₃.

In other embodiments, conductive substrate 210 may comprise atungsten-based and/or a tungsten-containing material formed in layers,such as tungsten-nitride (WN), for example, for use in a CERAM device orother type of CEM-based device. In embodiments, a WN substrate may beformed utilizing precursors such as tungsten hexacarbonyl (W(CO)₆)and/or cyclopentadienyltungsten(II) tricarbonyl hydride, both of whichmay comprise carbon as a dopant species. In another embodiment, a WNsubstrate may be formed utilizing triamminetungsten tricarbonyl((NH₃)₃W(CO)₃) and/or tungsten pentacarbonyl methylbutylisonitrile(W(CO)₅(C₅H₁₁NC), both of which may comprise carbon or nitrogen as adopant species. It should be noted that tungsten-based and/or tungstenprecursor materials may comprise dopant species in addition to nitrogenand/or carbon and claimed subject matter is not limited in this respect.Precursors may be used with nitrogen (e.g., co-flow) as a dopant speciesin the form of NH₃.

Forming or fabricating conductive substrate 210 may involve a variety ofprocesses, such as atomic layer deposition, chemical vapor deposition,plasma chemical vapor deposition, sputter deposition, physical vapordeposition, hot wire chemical vapor deposition, laser enhanced chemicalvapor deposition, laser enhanced atomic layer deposition, rapid thermalchemical vapor deposition or the like, and claimed subject matter is notlimited in this respect.

In an example, which will be described further in reference to FIGS.3A-3B, in a fabrication process involving TDMAT (tetrakis dimethylamidotitanium), which may be utilized to form a TiN substrate, an amount ofcarbon may remain embedded within a fabricated substrate as shown bydopant species atoms 205. Carbon may be embedded in a TiN substrate inthe form of, for example, one or more types of dopant species molecules,such as will be described further in reference to FIGS. 3A-3B. Thus,dopant species atoms 205 of FIG. 2A may represent carbon atoms that havedecomposed from dopant species molecules embedded within substrate 210.In an embodiment, an amount of carbon dopant remaining in a TiNsubstrate may be manipulated, for example, by increasing an amount ofTDMAT present in a deposition chamber. In other embodiments, atemperature utilized during a deposition process may be increased, whichmay influence decomposition, such as a rate of decomposition, of carbonfrom TDMAT. In other embodiments, a deposition process may utilize anincreased pressure, which may operate to increase “residence time” ofcarbon, for example, in a deposition chamber, which may, in turn,increase an amount of carbon present in a fabricated substrate. As theterm is used herein, “residence time” may refer to an amount of timethat a precursor or other agent persists in a process chamber. Residencetime may be increased in response to increasing pressure of a particularprecursor, or other agent, and/or may be increased responsive responseto an increase in a duration in which a precursor or other agent ispresent in a process chamber.

In another embodiment, in a fabrication process involving TICl₄(titanium tetrachloride), which may be utilized to form a TiN substrate,chlorine may remain embedded within substrate 210 in the form of one ormore types of dopant species molecule. Thus, in such an embodiment,dopant species atoms 205 of FIG. 2A may represent chlorine atoms thathave decomposed from dopant species molecules embedded within substrate210. In an embodiment, an amount of chlorine, as a dopant speciesremaining in a TiN substrate, may be manipulated, for example, byincreasing an amount of TiCl₄ present in a deposition chamber. In otherembodiments, a temperature utilized during a deposition process may beincreased, which may influence decomposition, such as a rate ofdecomposition, of chlorine from a TiCl₄ precursor, for example.

FIG. 2B is an illustration of an embodiment 225 of a correlated electronmaterial receiving dopant species atoms responsive to decomposition of aprecursor used to form a conductive substrate. As shown in FIG. 2B, ifCEM film 220 is formed over conductive substrate 210, an amount ofdopant species atoms 205 may diffuse from conductive substrate into CEMfilm 220. In particular embodiments, top layers of conductive substrate210 (e.g., layers closer to CEM film 220) may be fabricated using ahigher concentration of dopant-containing precursors, which may operateto make available additional dopant species atoms at layers only a smalldistance from CEM film 220.

In embodiments, diffusion of dopant species atoms 205 may be assisted byannealing a CEM film deposited over conductive substrate 210 at anelevated temperature, such as a temperature approximately in the rangeof 20° C. to 1000° C., for example. Annealing may operate to acceleratedecomposition of dopant species atoms from dopant species moleculesremaining within conductive substrate 210. Annealing may additionallyoperate to mend grain boundaries of a conductive substrate, which maypermit increased migration of dopant species atoms, such as chlorine,carbon, and nitrogen, for example, across adjacent grain boundaries.Annealing may also operate to increase pathways for dopant species atomsdiffusing from conductive substrate 210 to CEM film 220 in other ways,and claimed subject matter is not limited in this respect.

In particular embodiments, dopant species atoms and/or molecules, suchas nitrogen, chlorine, carbon, carbonyl, nitrosyl, and so forth, mayrepresent impurities that operate to adversely affect electricalperformance of conductive substrate 210. For example, additional carbonembedded in conductive substrate 210 may operate to decreaseconductivity (increase resistance) of conductive substrate 210.Accordingly, typical processes for preparing conductive substrates mayplace emphasis on removing carbon from conductive substrates. Otherprocesses may place emphasis on removing other impurities fromconductive substrates such as, for example, chlorine and nitrogen. Inaddition to potentially adversely affecting electrical conductivity ofthe substrate, impurities may also give rise to charge trapping, whichmay increase parasitic capacitance of conductive substrates. However, aswill also be discussed further in reference to FIGS. 3A-3B, suchimpurities in conductive substrates may enhance electrical performanceof CEM films such as, for example, by operating to bring aboutback-donation of electrons of compounds comprising NiO which maycomprise, for example, CEM film 220.

FIG. 2C is an illustration of an embodiment 250 of a conductive overlaydeposited over a CEM film. In embodiments, conductive overlay 230 maycomprise one or more materials similar to those comprising conductivesubstrate 210, such as one or more materials selected from a groupcomprising aluminum, cadmium, chromium, cobalt, copper, gold, iron,etc., and claimed subject matter is not limited in this respect. Afterfabrication of conductive overlay 230, one or more types of dopantspecies molecules, and/or dopant species atoms derived from one or moredopant species molecules, for example, may remain within conductivesubstrate 230. Thus, similar to fabrication of conductive substrate 210,a fabrication process involving TiCl₄, which may be utilized to formconductive overlay 230, may give rise to chlorine dopant speciesresponsive to decomposition of dopant species molecules derived fromTiCl₄.

In FIG. 2C, chlorine atoms, which may be formed responsive todecomposition of TiCl₄, for example, are shown as dopant species atoms206. In an embodiment, an amount of chlorine remaining in a conductiveoverlay comprising TiN may be manipulated, for example, by increasing anamount of TiCl₄ present in a deposition chamber utilized during theformation of conductive overlay 230. In other embodiments, a temperatureutilized during a deposition process may be increased, which mayinfluence a rate of decomposition of chlorine from a TiCl₄ precursor. Inother embodiments, residence time of chlorine present in a fabricatedsubstrate may be increased so as to increase presence of chlorine, forexample, embedded in a fabricated conductive overlay 230.

FIG. 2D is an illustration of an embodiment 275 of a CEM film receivingdopant species atoms responsive to decomposition of precursors used toform a conductive substrate and a conductive overlay. As shown in FIG.2D, if conductive overlay 230 is formed over CEM film 220, an amount ofdopant species atoms 206 may diffuse from conductive overlay 230 intoCEM film 220. In particular embodiments, top layers of conductiveoverlay 230 may be fabricated using a higher concentration ofdopant-containing precursors, which may operate to make availableadditional dopant species atoms at layers only a small distance from CEMfilm 220. In embodiments, diffusion of dopant species atoms 206 may beassisted by annealing a conductive overlay and CEM film deposited overconductive substrate 210 at elevated temperature, for example, which mayoperate to accelerate decomposition of dopant species atoms from adopant species molecules remaining within conductive overlay 230.Annealing may additionally operate to mend grain boundaries of aconductive overlay, which may permit increased migration of dopantspecies atoms, such as chlorine, carbon, and nitrogen, for example,across adjacent grain boundaries. Annealing may increase pathways fordopant species atoms diffusing from conductive overlay 230 to CEM film220 in other ways, and claimed subject matter is not limited in thisrespect.

FIG. 3A-3B is an illustration of an embodiment 300 of precursors, whichmay be utilized to form a conductive substrate along with one or moretypes of dopant species molecules. In FIG. 3A, precursor 310 correspondsto a TDMAT molecule, which may be utilized to form a TiN substrate, suchas substrate 210, of FIG. 2A, or may be utilized to form a conductiveoverlay, such as conductive overlay 230. In FIG. 3A, a nitrogen dopantspecies molecule in the form of NH₃, may be utilized in a co-flowprocess in which a conductive substrate or a conductive overlay, forexample, may be formed in layers by way of a deposition process.Precursors 310 and 320 may be utilized in an atomic layer depositionprocess or other suitable process utilized to form a TiN substrate, forexample, and claimed subject matter is not limited in this respect. Adeposition process, for example, may bring about formation of layers ofconductive material 330, which may comprise TiN as shown in FIG. 3A. Inother embodiments, however, substrate material 330 may comprise avariety of other materials, such as titanium nitride, platinum,titanium, copper, aluminum, cobalt, nickel, tungsten, tungsten nitride,cobalt silicide etc., and claimed subject matter is intended to embraceall types of conductive materials that may be used with correlatedelectron materials, for example.

After fabrication of substrate material 330, for example, dopant speciesmolecules 340 may remain embedded within substrate material 330. In theembodiment of FIG. 3A, dopant species molecules 340 may comprise a gas,such as nitrogen (N₂) and surface carbon-containing species 4HN(CH₃)₂,for example. It should be noted that other precursors may be utilized tofabricate other types of conductive materials, such as TDMAT, TDEAT,TTIP, PDMAT, TAETO, TaCl₅, W(CO)₆, (NH₃)3W(CO)₃, W(CO)5(C₅H₁₁NC), forexample, and claimed subject matter is not limited in this respect.Precursors utilized to fabricate other types of conductive materials maybring about dopant species molecules other than dopant species molecules340 of FIG. 3.

FIG. 3B is an illustration of an embodiment 350 of dopant speciesmolecules embedded in a conductive material diffusing into a CEM film.In FIG. 3B, carbon dopant species atoms are shown diffusing from adopant species molecule (4HN(CH₃)₂) into a CEM film 335 comprising NiO.In particular embodiments, diffusion of carbon dopant species atoms maypermit formation of carbonyl (CO), which may operate to fill oxygenvacancies in, for example, a CEM films comprising NiO to form NiO:CO.Such filling of oxygen vacancies, for example, in CEM film layers 345,may bring about electron back-donation in a CEM film. Back-donation maybe reversed, in a CEM film comprising nickel oxide, for example, (e.g.,NiO:CO), which may thereby permit the CEM film to switch to exhibiting ahigh-impedance property during device operation. Likewise, in FIG. 3Bnitrogen dopant species atoms are shown diffusing from a dopant speciesmolecule (N₂) to form NH₃, which may operate to fill oxygen vacancies inCEM film layers 345 of a CEM film comprising NiO, to form NiO:NH₃. Incertain embodiments, back-donation in a correlated electron material,for example, may occur responsive to use of nitrogen as a dopant speciesin the form of ammonia (NH₃), for example. As previously describedherein, electron back-donation may bring about controllable andreversible donation of electrons to a conduction band of a transitionmetal or transition metal oxide, such as nickel, for example, duringoperation.

FIG. 4 is a flowchart of an embodiment 400 for a generalized process forfabricating correlated electron materials with reduced interfacial layerimpedance. Example implementations, such as described in FIG. 4, andother figures described herein, may include blocks in addition to thoseshown and described, fewer blocks, or blocks occurring in an orderdifferent than may be identified, or any combination thereof. Embodiment400 may begin at block 410, which may comprise forming a conductivesubstrate using one or more precursors. At block 410, a substrate, suchas a conductive substrate comprising TiN may be formed. In otherembodiments, a conductive substrate may comprise platinum, titanium,copper, aluminum, cobalt, nickel, tungsten, tungsten nitride, cobaltsilicide, ruthenium oxide, chromium, gold, palladium, indium tin oxide,tantalum, silver, iridium, or any combination thereof. A conductivesubstrate formed at block 410 may involve a variety of processes, suchas atomic layer deposition, chemical vapor deposition, plasma chemicalvapor deposition, sputter deposition, physical vapor deposition, hotwire chemical vapor deposition, laser enhanced chemical vapordeposition, laser enhanced atomic layer deposition, rapid thermalchemical vapor deposition or the like, utilized in fabrication of CEMdevices.

At block 420, a CEM film may be formed over the conductive substrate. ACEM film may comprise a transition metal oxide comprising nickel, forexample, but may comprise other transition metals, transition metalcompounds, and/or transition metal oxides, such as aluminum, cadmium,chromium, cobalt, copper, gold, iron, manganese, mercury, molybdenum,nickel palladium, rhenium, ruthenium, silver, tin, titanium, vanadium.In particular embodiments, compounds that comprise more than onetransition metal oxide may also be utilized, such as yttrium titanate(YTiO₃).

Block 430 may comprise doping a CEM film via diffusing a first dopantspecies, derived from the one or more precursors, into the CEM film.Doping may include annealing a CEM film, which may operate to mend grainboundaries of a conductive substrate to permit increased migration ofdopant species atoms, such as chlorine, carbon, and nitrogen, ormolecular combinations, for example, across adjacent grain boundaries.Annealing may increase pathways for dopant species diffusing from aconductive substrate to a CEM film in other ways, and claimed subjectmatter is not limited in this respect.

FIG. 5 is a flowchart of an embodiment 500 for a generalized process forfabricating correlated electron materials with reduced interfacial layerimpedance. At block 510, one or more layers of CEM film may be formedover a substrate. In an embodiment, a CEM film may comprise one or morematerials previously described herein, and claimed subject matter is notlimited in this respect. At block 520, one or more conductive materialsmay be formed over the one or more layers of correlated electronmaterial. In embodiments, a conductive material may operate as anelectrode comprising TiN, platinum, copper, aluminum, and so forth.Block 530 may involve doping the correlated electron material film withone or more dopant species derived from one or more precursors utilizedin formation of the conductive substrate or the conductive overlay, or acombination thereof. Doping the CEM film and the conductive overlay mayinvolve annealing the conductive overlay and the CEM film to increasepathways for dopant species atoms or molecules diffusing from aconductive overlay to a CEM film, for example.

In particular embodiments, such as those previously described herein,plurality of CEM devices may be formed to bring about integrated circuitdevices, which may include, for example, a first correlated electrondevice having a first CEM and a second correlated electron device havinga second correlated electron material, wherein the first and second CEMsmay comprise substantially dissimilar impedance characteristics. Also,in an embodiment, a first CEM device and a second CEM device, may beformed within a particular layer of an integrated circuit. Further, inan embodiment, forming the first and second CEM devices within aparticular layer of an integrated circuit may include forming the CEMdevices at least in part by selective epitaxial deposition. In anotherembodiment, the first and second CEM devices within a particular layerof the integrated circuit may be formed at least in part by ionimplantation, such as to alter impedance characteristics for the firstand/or second CEM devices, for example.

Also, in an embodiment, two or more CEM devices may be formed within aparticular layer of an integrated circuit at least in part by atomiclayer deposition of a CEM. In a further embodiment, one or more of aplurality of correlated electron switch devices of a first correlatedelectron switch material and one or more of a plurality of correlatedelectron switch devices of a second correlated electron switch materialmay be formed, at least in part, by a combination of blanket depositionand selective epitaxial deposition. Additionally, in an embodiment,first and second access devices may be positioned substantiallyadjacently to first and second CEM devices, respectively.

In a further embodiment, one or more of a plurality of CEM devices maybe individually positioned within an integrated circuit at one or moreintersections of electrically conductive lines of a first metallizationlayer and electrically conductive lines of a second metallization layer,in an embodiment. One or more access devices may be positioned at arespective one or more of the intersections of the electricallyconductive lines of the first metallization layer and the electricallyconductive lines of the second metallization layer, wherein the accessdevices may be paired with respective CEM devices, in an embodiment.

In the preceding description, in a particular context of usage, such asa situation in which tangible components (and/or similarly, tangiblematerials) are being discussed, a distinction exists between being “on”and being “over.” As an example, deposition of a substance “on” asubstrate refers to a deposition involving direct physical and tangiblecontact without an intermediary, such as an intermediary substance(e.g., an intermediary substance formed during an intervening processoperation), between the substance deposited and the substrate in thislatter example; nonetheless, deposition “over” a substrate, whileunderstood to potentially include deposition “on” a substrate (sincebeing “on” may also accurately be described as being “over”), isunderstood to include a situation in which one or more intermediaries,such as one or more intermediary substances, are present between thesubstance deposited and the substrate so that the substance deposited isnot necessarily in direct physical and tangible contact with thesubstrate.

A similar distinction is made in an appropriate particular context ofusage, such as in which tangible materials and/or tangible componentsare discussed, between being “beneath” and being “under.” While“beneath,” in such a particular context of usage, is intended tonecessarily imply physical and tangible contact (similar to “on,” asjust described), “under” potentially includes a situation in which thereis direct physical and tangible contact, but does not necessarily implydirect physical and tangible contact, such as if one or moreintermediaries, such as one or more intermediary substances, arepresent. Thus, “on” is understood to mean “immediately over” and“beneath” is understood to mean “immediately under.”

It is likewise appreciated that terms such as “over” and “under” areunderstood in a similar manner as the terms “up,” “down,” “top,”“bottom,” and so on, previously mentioned. These terms may be used tofacilitate discussion, but are not intended to necessarily restrictscope of claimed subject matter. For example, the term “over,” as anexample, is not meant to suggest that claim scope is limited to onlysituations in which an embodiment is right side up, such as incomparison with the embodiment being upside down, for example. Anexample includes a flip chip, as one illustration, in which, forexample, orientation at various times (e.g., during fabrication) may notnecessarily correspond to orientation of a final product. Thus, if anobject, as an example, is within applicable claim scope in a particularorientation, such as upside down, as one example, likewise, it isintended that the latter also be interpreted to be included withinapplicable claim scope in another orientation, such as right side up,again, as an example, and vice-versa, even if applicable literal claimlanguage has the potential to be interpreted otherwise. Of course,again, as always has been the case in the specification of a patentapplication, particular context of description and/or usage provideshelpful guidance regarding reasonable inferences to be drawn.

Unless otherwise indicated, in the context of the present disclosure,the term “or” if used to associate a list, such as A, B, or C, isintended to mean A, B, and C, here used in the inclusive sense, as wellas A, B, or C, here used in the exclusive sense. With thisunderstanding, “and” is used in the inclusive sense and intended to meanA, B, and C; whereas “and/or” can be used in an abundance of caution tomake clear that all of the foregoing meanings are intended, althoughsuch usage is not required. In addition, the term “one or more” and/orsimilar terms is used to describe any feature, structure,characteristic, and/or the like in the singular, “and/or” is also usedto describe a plurality and/or some other combination of features,structures, characteristics, and/or the like. Furthermore, the terms“first,” “second,” “third,” and the like are used to distinguishdifferent aspects, such as different components, as one example, ratherthan supplying a numerical limit or suggesting a particular order,unless expressly indicated otherwise. Likewise, the term “based on”and/or similar terms are understood as not necessarily intending toconvey an exhaustive list of factors, but to allow for existence ofadditional factors not necessarily expressly described.

Furthermore, it is intended, for a situation that relates toimplementation of claimed subject matter and is subject to testing,measurement, and/or specification regarding degree, to be understood inthe following manner. As an example, in a given situation, assume avalue of a physical property is to be measured. If alternativelyreasonable approaches to testing, measurement, and/or specificationregarding degree, at least with respect to the property, continuing withthe example, is reasonably likely to occur to one of ordinary skill, atleast for implementation purposes, claimed subject matter is intended tocover those alternatively reasonable approaches unless otherwiseexpressly indicated. As an example, if a plot of measurements over aregion is produced and implementation of claimed subject matter refersto employing a measurement of slope over the region, but a variety ofreasonable and alternative techniques to estimate the slope over thatregion exist, claimed subject matter is intended to cover thosereasonable alternative techniques, even if those reasonable alternativetechniques do not provide identical values, identical measurements oridentical results, unless otherwise expressly indicated.

It is further noted that the terms “type” and/or “like,” if used, suchas with a feature, structure, characteristic, and/or the like, using“optical” or “electrical” as simple examples, means at least partiallyof and/or relating to the feature, structure, characteristic, and/or thelike in such a way that presence of minor variations, even variationsthat might otherwise not be considered fully consistent with thefeature, structure, characteristic, and/or the like, do not in generalprevent the feature, structure, characteristic, and/or the like frombeing of a “type” and/or being “like,” (such as being an “optical-type”or being “optical-like,” for example) if the minor variations aresufficiently minor so that the feature, structure, characteristic,and/or the like would still be considered to be predominantly presentwith such variations also present. Thus, continuing with this example,the terms optical-type and/or optical-like properties are necessarilyintended to include optical properties. Likewise, the termselectrical-type and/or electrical-like properties, as another example,are necessarily intended to include electrical properties. It should benoted that the specification of the present disclosure merely providesone or more illustrative examples and claimed subject matter is intendedto not be limited to one or more illustrative examples; however, again,as has always been the case with respect to the specification of apatent application, particular context of description and/or usageprovides helpful guidance regarding reasonable inferences to be drawn.

In the preceding description, various aspects of claimed subject matterhave been described. For purposes of explanation, specifics, such asamounts, systems, and/or configurations, as examples, were set forth. Inother instances, well-known features were omitted and/or simplified soas not to obscure claimed subject matter. While certain features havebeen illustrated and/or described herein, many modifications,substitutions, changes, and/or equivalents will occur to those skilledin the art. It is, therefore, to be understood that the appended claimsare intended to cover all modifications and/or changes as fall withinclaimed subject matter.

1-14. (canceled)
 15. A switching device, comprising: an electrodecomprising at least one layer of electrically conductive material; and acorrelated electron material formed on the electrode, wherein thecorrelated electron material comprises a dopant species derived from oneor more precursors utilized in formation of the at least one layer ofelectrically conductive material.
 16. The switching device of claim 15,wherein the dopant species operates to fill oxygen vacancies in anelectron back-donating material of the correlated electron material. 17.The switching device of claim 15, wherein a concentration of an electronback-donating material of the correlated electron material comprises anatomic concentration of between 0.1% and 10.0%.
 18. The switching deviceof claim 15, wherein the correlated electron material comprises nickeloxide.
 19. The switching device of claim 18, wherein the electricallyconductive material comprises titanium nitride, tantalum nitride ortungsten nitride, or any combination thereof.
 20. A switching device,comprising: an electrically conductive substrate; a correlated electronmaterial deposited over the electrically conductive substrate; anelectrically conductive overlay deposited over the correlated electronmaterial, wherein the correlated electron material comprises a dopantspecies derived from one or more precursors utilized in formation of theelectrically conductive substrate or utilized in formation of theelectrically conductive overlay, or a combination thereof.
 21. Theswitching device of claim 20, wherein the dopant species comprisesnitrogen, chlorine or carbon, or any combination thereof.
 22. Theswitching device of claim 20, wherein the dopant species operates tofill oxygen vacancies in the correlated electron material.
 23. Theswitching device of claim 20, wherein the electrically conductivesubstrate comprises titanium nitride, tantalum nitride or tungstennitride, or any combination thereof.
 24. The switching device of claim20, wherein the correlated electron material comprises nickel oxide. 25.The switching device of claim 20, wherein the correlated electronmaterial comprises an electron back-donating material.
 26. The switchingdevice of claim 25, wherein the correlated electron material comprises aconcentration of the electron back-donating material having an atomicconcentration of between 0.1% and 10.0%.
 27. The switching device ofclaim 20, wherein the electrically conductive overlay comprises titaniumnitride, tantalum nitride or tungsten nitride, or any combinationthereof.
 28. The switching device of claim 15, wherein the dopantspecies comprises carbon, chlorine, nitrogen, fluorine, cyanide (CN),nitrosyl (NO), ammonia (NH3), oxynitride molecules (NxOy, wherein x andy comprise whole numbers and wherein x>0 and y>0) or molecules of theform CxHyNz (wherein x>0, y>0, z>0), or any combination thereof.
 29. Theswitching device of claim 15, wherein the correlated electron materialfurther comprises an additional dopant species derived from the one ormore precursors utilized in formation of the electrically conductivesubstrate or utilized in formation of the electrically conductiveoverlay, or a combination thereof.
 30. The switching device of claim 20,wherein the dopant species comprises carbon, chlorine, nitrogen,fluorine, cyanide (CN), nitrosyl (NO), ammonia (NH3), oxynitridemolecules (NxOy, wherein x and y comprise whole numbers and wherein x>0and y>0) or molecules of the form CxHyNz (wherein x>0, y>0, z>0), or anycombination thereof.
 31. The switching device of claim 20, wherein thecorrelated electron material further comprises an additional dopantspecies derived from the one or more precursors utilized in formation ofthe electrically conductive substrate or utilized in formation of theelectrically conductive overlay, or a combination thereof.